Cryptic Arthropod Infestations Affecting Humans BENJAMIN KEH, MS, and ROBERT S
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192 Clinical Mledicline Cheyletiella blakei, an Ectoparasite of Cats, as Cause of Cryptic Arthropod Infestations Affecting Humans BENJAMIN KEH, MS, and ROBERT S. LANE, PhD, Berkeley, and SHERRY P. SHACHTER, DVM, Alameda, California Cheyletiella blakei, an ectoparasitic mite of domestic cats, can cause an extremely annoying, persis- tent and pruritic dermatosis of obscure origin (cryptic infestation) in susceptible persons having close contact with infested cats. Although the prevalence ofcheyletiellosis in humans andcats appears to be low, evidence of its occurrence in California is increasing. Cheyletiellosis is often underdiagnosed in both its natural host and in humans. The small size of the mite, lack of publicity about the disease, frequentabsence ofsymptoms in infested cats andfailure to recover the mite from humans contribute to its delayedrecognition. When C blakei or other mites are suspectedofbeing the cause ofa dermatosis, medical entomologists may help to hasten the diagnosis by examining the patient's physical surround- ings, potential vertebrate hosts and other sources for the presence of mites. After C blakei has been eliminatedfrom cats with an appropriate pesticide, the disease in humans is self-limiting. (Keh B, Lane RS, Shachter SP: Cheyletiella blakei, an ectoparasite of cats, as cause of cryptic arthropod infestations affecting humans. West J Med 1987 Feb; 146:192-194) Several mites including Cheyletiella blakei, * a widely dis- be aware of its existence. The frequent lack of obvious symp- tributed ectoparasite of domestic cats, are capable of toms in the natural host, the domestic cat, also contributes to causing cryptic infestations in humans. 1-3 This mite and the the failure of patients to recognize the specific cause of their related Cheyletiella yasguri on dogs produce a skin condition dermatitis. In our experience and that of others, dermatoses referred to as cheyletiellosis. We refer to such infestations on caused by Cheyletiella mites are commonly underdiagnosed humans caused by either species as human cheyletiellosis, on in patients.410 cats caused by C blakei as feline cheyletiellosis and on dogs The first published account of the occurrence of C blakei caused by Cyasguri as canine cheyletiellosis. in California appeared in 1975.6 In that infestation, a mother Typically, members of a household in which one or more and her 5-year-old daughter were afflicted with the disease in infested cats live report persistent pruritic lesions (see below) Berkeley, Alameda County, in July 1974. Since then three but are unaware oftheir cause until Cblakei is found weeks or additional infestations involving one to five persons have months later. After this mite is eliminated from a cat, mem- come to our attention. These include cases in Palo Cedro, bers ofthe household recover quickly without treatment-that Shasta County (April 1979), Petaluma, Sonoma County (Au- is, the disease is self-limiting.4-8 gust 1979), and Berkeley (March 1985). The Shasta and Recovery of Cblakei from cats (or Cyasguri from dogs) is Sonoma County records are from the files of the California essential for establishing a diagnosis ofhuman cheyletiellosis. State Department ofHealth Services and were made available To our knowledge there has been no published account in to us through the courtesy ofMr Gail Grodhaus. which a diagnosis of this disease was made on the basis of The purpose of this communication is to alert the medical clinical evidence alone. Moreover, when a patient is unable to community to increasing evidence of C blakei occurrence in provide a clue as to the probable cause of the pruritus, and California, to present detailed case history information about when veterinarians do not detect the mite on a cat, the com- the latest outbreak, to summarize some of the difficulties in- plaint goes undiagnosed. herent in diagnosing human and feline cheyletielloses and to Among factors that tend to obscure the cause of feline call attention to methods used by medical entomologists in cheyletiellosis is the small size ofthe mite, which ranges to as investigating cryptic arthropod infestations. much as 500 microns in body length. Thus, the mites are Report of an Outbreak scarcely visible to the naked eye and are easily overlooked.8 9 Further, very few lay persons or medical practitioners seem to The patient, aged 44 years, her husband and a daughter live in Berkeley, California. They purchased a 4-month-old *Cheyletiella parasitivorax was originally the name applied to Cheyletiella mites white female Persian cat from a dealer in San Francisco in found on rabbits, cats and dogs. Smiley (Proc Entomol Soc Wash 1965; 67:75-79) mid-December 1984. About four weeks later the mother recognized Cheyletiella on cats as a distinct species and later likewise (Ann Entomol Soc Am 1970; 63:1056-1078) recognized Cheyletiella on dogs as distinct. Cparasi- began having pruritus that occurred daily during the late after- livorax remains one of two Cheyletiella species occurring on rabbits. noon. In early February she traveled out of the country and From the Department of Entomological Sciences, University of California, Berkeley (Dr Lane), and the South Shore Pet Hospital, Alameda, California (Dr Shachter). Mr Keh has recently retired from the Vector Surveillance and Control Branch, California State Department ofHealth Services, Berkeley, Califomia. Reprint requests to Robert S. Lane, PhD, Department of Entomological Sciences, University ofCalifornia, Berkeley, CA 94720. e o o THE WESTERN JOURNALTHE WESTERNJOURNALOF MEDICINE * FEBRUARY 1987 14619872 * 146 * 2193~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~193 her symptoms ceased but resumed on her return three weeks Epidemiology and Diagnosis later. Existing data suggest that C blakei is probably cosmopol- Affected parts of her body included the breasts and ante- itan in distribution,11 is host-specific on cats"I and completes rior trunk down to the waist, the back and occasionally the its entire life cycle on cat fur and skin. 12 Its life away from its arms and legs. The lesions were urticarial papules that typi- host (on humans or in the environment) is transitory. The cally occurred in clusters of three or four. According to the possibility that free-living C blakei may occasionally cause patient, they were first observed soon after the onset of pru- dermatitis in susceptible persons cannot be discounted. Le- ritus and resembled mosquito bites. Rapid swelling and irrita- sions may develop in casual visitors to a home having an tion occurred in some affected areas, though other areas did infested cat without having direct contact with the cat either not react until the following day. She had difficulty breathing before the animal is treated or for a brief period afterward. 12 and experienced emotional distress. The lesions disappeared This possibility is suggested indirectly by a case involving C slowly over a period ofweeks. yasguri in which a child had hundreds of pruritic lesions after Her 7-year-old daughter was similarly, albeit less se- it had slept on a quilt used by an infested dog13 and, in another verely, affected. Her husband had a few lesions and reacted case, when the same mite was recovered from the floor, furni- only slightly. Similar lesions developed in two children who ture and a mattress. 4 were overnight guests, and the children reacted severely. There appears to be no authoritative explanation of how The mother consulted six physicians including three der- human skin lesions due to C blakei are produced. In some matologists, but was unsuccessful in obtaining a correct diag- instances, however, the distribution of skin lesions on the nosis. She had been treated with topical and systemic trunk and other body regions is noted to coincide with areas in administration of steroids and had transitory relief. The pa- contact with the infested cat. This observation suggests that tient strongly suspected that an unidentified arthropod was the the lesions are caused by bites ofthe mites. cause of her pruritus and reported that on one occasion the Not surprisingly, once an etiologic agent is recognized, pruritus had been more severe after her cat had shared her reports of its occurrence increase. Bjarke and co-workers8 bed. Additionally, on more than one occasion, pruritus and saw 37 cases ofhuman cheyletiellosis in a two-year period. In papular formation began within about 30 minutes after she California, canine and feline cheyletielloses are being seen had held her cat. Scabies had been ruled out but flea bites and with increasing frequency.'0 The true incidence ofthe disease hives were still being considered in the differential diagnosis in humans and pets in this state (and elsewhere in the western when a medical entomologist (R.S.L.) was contacted for as- United States) is not known, but it is probably not as un- sistance on March 21, 1985. common as suggested by the dearth of reports from this re- The asymptomatic cat had been treated with a bath of gion. 0.06% pyrethrins and 0.6% piperonyl butoxide (Theradex) Patients usually are of little help in providing information without apparent success. Two of us (R.S.L. and S.P.S.) on the probable source oftheir dermatitis. Bjarke and associ- subsequently examined the cat for Cheyletiella mites by first ates8 in referring to human cheyletiellosis said that among 37 treating it with a pyrethroid wash, 0.05% tetramethrin patients in 24 homes "only in two cases did the owners them- (Aqua-Methrin), and then brushing it with a toothbrush along selves suspect their dogs or cats as being the indirect cause of the spine and on both flanks anteriorly to the neck and posteri- their itching dermatitis." Thus, patients would very likely orly to the base of the tail. The brushing was examined in the seek the help ofa physician first rather than a veterinarian. laboratory (by R.S.L.) and 16 mites, identified as C blakei, If C blakei is not suspected as the cause of dermatosis in were found.